diff options
Diffstat (limited to 'llvm_mode/README.llvm')
| -rw-r--r-- | llvm_mode/README.llvm | 37 |
1 files changed, 29 insertions, 8 deletions
diff --git a/llvm_mode/README.llvm b/llvm_mode/README.llvm index dc860e97..77c406f8 100644 --- a/llvm_mode/README.llvm +++ b/llvm_mode/README.llvm @@ -38,8 +38,8 @@ co-exists with the original code. The idea and much of the implementation comes from Laszlo Szekeres. -2) How to use -------------- +2) How to use this +------------------ In order to leverage this mechanism, you need to have clang installed on your system. You should also make sure that the llvm-config tool is in your path @@ -69,20 +69,41 @@ operating mode of AFL, e.g.: Be sure to also include CXX set to afl-clang-fast++ for C++ code. The tool honors roughly the same environmental variables as afl-gcc (see -../docs/env_variables.txt). This includes AFL_INST_RATIO, AFL_USE_ASAN, -AFL_HARDEN, and AFL_DONT_OPTIMIZE. +../docs/env_variables.txt). This includes AFL_USE_ASAN, +AFL_HARDEN, and AFL_DONT_OPTIMIZE. However AFL_INST_RATIO is not honored +as it does not serve a good purpose with the more effective instrim CFG +analysis. Note: if you want the LLVM helper to be installed on your system for all users, you need to build it before issuing 'make install' in the parent directory. -3) Gotchas, feedback, bugs +3) Options + +Several options are present to make llvm_mode faster or help it rearrange +the code to make afl-fuzz path discovery easier. + +If you need just to instrument specific parts of the code, you can whitelist +which C/C++ files to actually intrument. See README.whitelist + +For splitting memcmp, strncmp, etc. please see README.laf-intel + +As the original afl llvm_mode implementation has been replaced with +then much more effective instrim (https://github.com/csienslab/instrim/) +there is an option for optimizing loops. This optimization shows which +part of the loop has been selected, but not how many time a loop has been +called in a row (unless its a complex loop and a block inside was +instrumented). If you want to enable this set the environment variable +LOOPHEAD=1 + + +4) Gotchas, feedback, bugs -------------------------- This is an early-stage mechanism, so field reports are welcome. You can send bug reports to <afl-users@googlegroups.com>. -4) Bonus feature #1: deferred instrumentation +5) Bonus feature #1: deferred instrumentation --------------------------------------------- AFL tries to optimize performance by executing the targeted binary just once, @@ -129,7 +150,7 @@ will keep working normally when compiled with a tool other than afl-clang-fast. Finally, recompile the program with afl-clang-fast (afl-gcc or afl-clang will *not* generate a deferred-initialization binary) - and you should be all set! -5) Bonus feature #2: persistent mode +6) Bonus feature #2: persistent mode ------------------------------------ Some libraries provide APIs that are stateless, or whose state can be reset in @@ -169,7 +190,7 @@ PS. Because there are task switches still involved, the mode isn't as fast as faster than the normal fork() model, and compared to in-process fuzzing, should be a lot more robust. -6) Bonus feature #3: new 'trace-pc-guard' mode +8) Bonus feature #3: new 'trace-pc-guard' mode ---------------------------------------------- Recent versions of LLVM are shipping with a built-in execution tracing feature |